Relationship between the Synthesis of Prussian Blue Pigments, Their Color, Physical Properties, and Their Behavior in Paint Layers

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• 作者：Louise Samain ; Fernande Grandjean ; Gary J. Long ; Pauline Martinetto ; Pierre Bordet ; David Strivay
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：May 16, 2013
• 年：2013
• 卷：117
• 期：19
• 页码：9693-9712
• 全文大小：880K
• 年卷期：v.117,no.19(May 16, 2013)
• ISSN：1932-7455

文摘

Prussian blue pigments, highly insoluble mixed-valence iron(III) hexacyanoferrate(II) complexes of typical stoichiometry Fe₄^III[Fe^II(CN)₆]₃路xH₂O or KFe^III[Fe^II(CN)₆]路xH₂O, have been used as pigments in oil paintings and watercolors for 300 years. For poorly understood reasons, these pigments often fade with time. Although the preparation methods have been recognized since the mid-eighteenth century as a contributory factor in the fading of the pigment, the spectral and physical properties of Prussian blue that vary with the type of synthesis were not precisely identified. Several Prussian blue pigments have been prepared by different methods and characterized by thermogravimetric analyses, high-energy powder X-ray diffraction, atomic absorption and flame emission, UV鈥搗isible, iron-57 M枚ssbauer, iron K-edge X-ray absorption, and Raman spectroscopy. The type of synthesis influences the hue, tinting strength, and hiding power properties of the Prussian blue pigments. Two major features appear to be strongly dependent on the preparative methods, the particle size and the local disorder. Both a nitrogen atmosphere and an intermediate aging step of the Berlin white, Fe₂^II[Fe^II(CN)₆], during the synthesis are required to obtain a highly colored pigment through the optimization of particle size, minimization in the perturbations to the Fe^II鈥揅N鈥揊e^III intervalence electron transfer pathway, and the minimization of disordered vacancies. The potassium containing Prussian blue structure has been revisited. It can be described with the Pm3m space group, where approximately one-quarter of the [Fe^II(CN)₆]^{4鈥?/sup> sites are vacant and where the potassium cation is located at a zeolitic-like position inside the lattice cavities. The degree of ordering of the [FeII(CN)₆]4鈥?/sup> vacancies in all Prussian blues was quantified using atomic pair distribution analysis, an ordering that is consistent with the iron K-edge X-ray absorption spectra. The presence of strain in the crystals is observed by both powder X-ray diffraction and M枚ssbauer spectroscopy. The structural similarity between the alkali-free, improperly referred to as 鈥渋nsoluble鈥? and the alkali containing, 鈥渟oluble鈥? Prussian blues may explain why the two varieties are almost undistinguishable by spectroscopic techniques.}